Electron tube grid structure



Aug. 3, w. W EIT-EL ELECTRON TUBE GRID STRUCTURE FiledJan. 25, 1946'INVENToR WILL/AM W. El EL.

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Patented Ang. 3, 1948 1 2,446.27; nxcrnoh 'runs Gum srnUc'rUns wnum w.nml, Woodside, cuir., assigner u Enel-McCullough, .Inc.,- ,San Bruno,Calif., corporationf Califol'niaE anuuumniinm zsgdsis, serial No.642,944

solaire.. wisse-215i' Hy invention relates to an electron tube havingparallel planmelectrodesi.

One ofthe .principal problems in tubes having planar electrodes withclose spacings .isto maintain the grid wiresj'in a commonV plane andpre` vent grid distortion due to warping and sagging of the wires under'heat during operation of the tube, which deformation alters theelectrode spacing: and thereby changes the operating characteristics oftube, causingfrequency drift and other undesirable effects. 'Y The broadoblect of my invention is to provide an improved grid structure in-atube of the character described,V sothat initial spacings betweenelectrodesare accurately maintained during operation of the tulle.

-A more specific object includes the provision, in a grid having amultiplicity of parallel grid wires, of means for retaining the wires ina commonplane. j

Another object is to provide a grid of the character described embodyingimprovements whereby problems ofgrid warpage. spot heating and gridemission are alleviated.

A further object is to provide an improved methodof fabricating a gridstructure.

The invention es otheroblects and features of advantage, some of which,with the foregoing, will be set forth in the following, description ofmy invention. It is to be understood :thatI do not limit myself to thisdisclosure of.: species of my invention-ail may adopt variantembodiments thereof withlnthescope ofthe claims.

Referring to the drawing: f

Figure 1 is an axial sectional view of a tube embodying mylnvention; and

Figure 2 is j. grid, portions of thestructure being omitted forsimplicity. l l

Figure 3 is enlarged detail view showing an intersection ofegrid wires.

In terms of-s oad inclusion, my electron tube embodies a gri having amultiplicity of closely spaced main wires lying in a common planepresenting a flat grid surface, and a wire disposed transversely of the-first mentioned wires and lying fiat against the grid surface. In mypreferred structure, several transverse wires are provided, spaced rnorewidely apart vthan the main grid wires. The transverse wires arepreferably bonded to the main.wlres at the 'intersections thereof. Ina.triode having my improvedgrid interposed between an anode and cathode,the grid -is preferably positioned with the vtransverse wires on thesurface facing the anode.

plan view looking down at the In greater detail, and referring tothedrawing, my improvements are illustrated by a triode structurecomprising an anode 2, grid l and cathode arrangedjwith active surfacesdisposed in parallel planes.4 These electrodes are mounted in a"suitable envelope structure, that chosen lfor illustration comprising abody sections of vitreous material. such as glass. sealed at one end toan anode supporting member 1 and at the other -enel to a tubularenvelope section l. Anode support 1 'also functions as the anodeterminal andcomprises a metal cup having a cylindrical wall l extendingfrom a flange ll to which the glass is sealed. Anode 2 is secured toneck l2 of the support by braze l2.

' The anode is preferably of metal'lhaving good heat conductivity, suchas copper, 'with a fiat anode surface presented interiorly of theenvelope and having a stem portion I4 extending outwardly oftheenvelope. A suitable cooler is 'provided on the anode, preferablycomprising a metal core II fitted on stem Il Vand carrying a series oftransverse disk-like heat radiating ilns l1 separated by spacing ringsIl, the fins and spacers being clamped together by a crimped lip IQ oncore ll,

The tube is exhausted through a metal tubulation 2l secured to anodestem Il by braze il and communicating with a passage 22 ported into theenvelope through opening 23. After exhaust, the tube is sealed bypinching off the tubulation at tip 24.

Envelope section l at the opposite end of the envelope is acylindrically shaped metallic mem- `ber having an outturned flange 28to` which glass body section l is sealed. Section 2 1" is arrangedcoaxially with the anode and also functions as the terminal for grid l.outer end of tubular section I is open, whereby the' grid and cathodestructures may be inserted through this end of the envelope.

Grid 2 is supported on a. sleeve* 21 of metal having good heatconductivity. such as copper, insertable in envelope section 8. l Thesection l and sleeve 21 are shaped and proportioned to provide limitstops to establish a predetermined spacing between the grid and anode.This is preferably accomplished by an offsetportion 2l on section lproviding an annular seat engageable by alllp formed by an offsetportion ll on sleeve 2 1.

Cathode I is mounted on a stem I2 4also coaxial with the anode andarranged to project into the envelope through tubular section I. Thecathode stem comprises a pair of concentric stem members including anouter tubular part 33 and an inner rod-like part 34. These stem membersDuring assembly, the

tween rod Il and the lower end of a sleeve Il.

which sleeve is fitted into stem member and secured thereto by braze ll.For convenience in making connection with the inner stem member. a.cup-shaped terminal Il is preferably fixed to the outer end of rod lland spaced from the outer stem member by-insulator.

The cathode comprises a cylindrical can l2 having a flat top carryingthe active coating which may be of the usual oxide type commonly usedfor indirectly heated cathodes. Can l! is coaxial with and secured tothe inner end of stem member Il. The cathode heater comprises a spiral4I having one end connected to stem member Il lby-bracket M and theother end connected to stem member Il by bracket 4l. l Suitable hainesI1 and 4l arranged in can 42 serve to confine the heat and direct ittoward the active surface of the cathode.

. The cathode structure is supported from envelope section l by aU-shaped metallic sleeve having an outer flange 4l and an inner flangeIl, this cathode supporting sleeve being fitted into section I in nestedrelation to grid support-a ing sleeve 21. A vitreous `ring 52 is sealedbetween stem member and inturned lip 53 on sleeve flange il. A shield Mon the stem above glass ring 52 serves to direct the latter against heatand material sputtered from the cathode.

Cathode supporting sleeve El is also shaped and proportioned to providea limit stop to establish a predetermined spacing between the cathodeand grid, this being accomplished by utilizing the folded inner end ofthe sleeve as a lip for engaging the seat provided by offset portion Iiof the grid supporting sleeve. The various p arts are so proportionedthat the distance between the upper grid surface and the lip at oifsetll is less than that between the anode surface and the seat at inch anda grid-cathode spacing of .0045 inch have been satisfactorily made andused.

The final closure is made by a fused metallic bond It joining the outeradjacent edges of section l, sleeve 21 and sleeve flange Il. This bondmay be formed by welding or grazing to simultaneously join the threeedges together.

' While the tube structure above described is preferred, it isunderstood that my improved grid structure, hereinafter described, maybe incorpo- 'rated in any tube having planar type electrodes.

including tubes having more than one grid, the

triode illustrated being chosen for purposes of simplicity.

' As stated earlier herein, one of the principal problems in tubeshaving planar electrodes with close spacings is to maintain the gridwires in a common plane and prevent misalignment due to warping andsagging of the wires under heat dur-` ing operation of the tube, whichdeformation alters the operating characteristics of the tube. In thepast, grids of this type have been made with straight parallel wiressupported at the ends,

these grids being particularly bad because of relative warping betweenthe wires. Grids of mesh construction have also been used. embodyingwoven wires, but prefabricated'meshes are dim- 4 cult if not impossibleto mount on a support and insure uniform tautness of the individualwires in the mesh. A woven structure is also bad because the bendsformed in the individual wires of the mesh complicate the warpingproblem when the structure is subsequently heated.

My improved grid shown in Figures 1, 2 and 3 comprises a multiplicity ofstraight wires Il lying parallel in a common plane to present a flatgrid surface. These main grid bars are of small diameter and are closelyspaced, being preferably of a refractory metal wire such as molybdenumor tungsten, the latter being preferred. Main grid wires of .0018 inchdiameter spaced .006 inch apart have been satisfactorily used in a tubehaving electrode spacings of the character described. Grid wires I1 arestretched across and secured to a hat mounting ring Il, preferably oftungsten, adapted for fastening to a ange l on supporting sleeve f1.

A plurality of say three straight tungsten wires Il are disposedtransversely of wires i1 to lle fiat against the surface formed by themain grid wires. These secondary grid wires are preferably of the samematerial and diameter as the main grid bars and are stretched across andsecured to mounting ring 5I. Since the main and transverse grid bars areall straight wires they may be positioned across the mounting ring withuniformly applied tension. The transverse wires Il are bonded to each ofthe main wires Il at each intersection thereof. plished by a metalliccoating l2 over all of the lWires, which coating preferably extends overring [l to simultaneously braze the wires to the mounting ring. Coating82 is of a metal having lower melting point than that of the grid wiresand is preferably of a material, such as gold, acting as a suppresser ofelectron emission as well as a bonding agent.

My preferred method of making the grid is to place ring Il on a flatmandrel and wrap a tungsten wire about the mandrel to lay the multi-'plicity of gridbars 5l over the ring. Secondary lv'vi'res Il are thenlaid across the mandrel in a transverse direction. A ring-shaped pieceof gold wire is then placed over the wires on ring Il and the entireassembly is heated in hydrogen to flow the gold over the wires andmounting ring. The wires are then clipped about the periphery of ring t9free the completed grid from the mandrel. A series of grids may be madeon a single mandrel in this way. If desired, the transverse wires il maybe laid on first to underlie main wires I1.

'While three transverse wires il' are'shown. it is understood that moreor lessjnay be used, the spacing between the transverse wires beingoptional and, of course, much wider than that between the main wires. Inany event. but few of these secondary wires are required to performtheir function of reinforcing and cooling the main grid wires. Thetransverse wires serve as supporting straps to hold the main wires in acommon plane, and also serve as heat conductors to'aid in carrying heataway from the central portions of the grid. Both of these functionsoperate to prevent grid warpage. Bonding of the wires at theintersections helps from the standpoint of heat conduction as well aslhave no perceptible influence on the electrical characteristics of thegrid. Also. since the transverse wires lie flat against the main gridbars the latter are not disturbed from ltheir flat-lying This bonding isaccom- :Maan

planar relationship. As a result, the main grid bars present truly fiatgrid surfaces to the other electrodes. f

I claim:- j

1. In an electron tube having parallel plane electrodes, a gridcomprising a multiplicity of closely spaced parallel wires lying in acommon plane presenting a flat grid surface spaced from an adjacentelectrode, and a wire dsposed transf versely across the mid-portions ofthe flrst mentioned wires and lying flat against said surface, saidtransverse wire having a diameter less than the spacing between the gridand adjacent elec' trode.

2. A grid electrode for an electron tube conrprising a mounting ring, amultiplicity of closely spaced parallel wires extending across the ringand lying in a common plane presenting a flat grid surface, and aplurality of more widely spaced wires extending across said ring intransl.

verse relation to the rst mentioned wires and lying flat against saidsurface, said wires being bonded to the mounting ring and to each otherat the intersections thereof.

3. A grid electrode for an electron tube corri-l prising a mountingring. a multiplicity of closely spaced parallel wires extending acrossthe ring4 and lying in a common plane presenting a fiat grid surface, aplurality of more widely spaced wires extending across said ring intransverse relation to the first ,mentioned wires and lying fiat againstsaid surface, and a metallic coating on the electrode bonding said wiresto the mounting ring and to each other at the intersections thereof.

4. A grid electrode for an electron tube 'comprising a mounting ring, amultiplicity of closely spaced parallel wires of refractory metalextending across the ring and lying in a common plane presenting a atgrid surface, a plurality of more widely spaced wires of refractorymetal extending across said ring in transverse relation to the nrstmentioned wires and lying fiat against said surface, and a coatingon theelectrode of metal having a lower melting point than a 365,303

6 that of the wires bonding said wires to the mounting ring and to eachother at the intersections thereof.

5. A grid electrode for an electron tube comprising a mounting ring, amultiplicity of closely spaced parallel wires of tungsten extendingacross the ring and lying in' a common plane presenting a ,flat gridsurface, a plurality of more widely spaced wires of tungsten extendingacross said ring in transverse relation to the first mentioned wires andlying flat againstsaid surface, and a coating of gold on the elecrodebonding said wires to the mounting ring and to each other at theintersections thereof.

6. In an electron tube having parallel plane electrodes. a gridcomprising a 4multiplicity of closely spaced parallel wires lying in acommon plane presenting a flat grid surface spaced from an adjacentelectrode, and a plurality of more widely spaced wiresdisposedtransversely across the mid-portions of the first mentionedwires and lying 'ilat against said surface, said transverse wires havinga diameter less than the spacing between the grid and adjacentelectrode.

The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,472,505 Trimble Oct. 30, 19231,892,819 Van Gessel s Jan. 3, 1933 2,045,526 Harries June 23, 19362,047,369 Y Hickok July 14, 1936 2,338,036 Gorton Dec. 28, 19432,402,119 Beggs June 18, 1946 2,413,689 Clark et al. Jan. 7, 19472,415,360 McIntosh Feb. 4, 1947 FOREIGN PATENTS Number Country DateGreat Britain Jan. 21, 1932

